<template>
    <div class="pagination">
      <button :disabled="pageNo == 1" @click="$emit('getPageNo', pageNo-1)">上一页</button>
      <button v-if="startNumAndEndNum.start > 1" @click="$emit('getPageNo', 1)" :class="{active:pageNo==1}">1</button>
      <button v-if="startNumAndEndNum.start > 2">···</button>
  
      <button v-for="(page, index) in startNumAndEndNum.end" :key="index" v-if="page >= startNumAndEndNum.start" @click="$emit('getPageNo', page)" :class="{active:pageNo==page}">{{page}}</button>
      
      
      <button v-if="startNumAndEndNum.end < totalPage-1">···</button>
      <button v-if="startNumAndEndNum.end < totalPage" @click="$emit('getPageNo', totalPage)" :class="{active:pageNo==totalPage}">{{totalPage}}</button>
      <button :disabled="pageNo == totalPage" @click="$emit('getPageNo', pageNo+1)">下一页</button>
      
      <button style="margin-left: 30px">共 {{total}} 条</button>
    </div>
  </template>
  
  <script>
    export default {
      name: "Pagination",
      props: ['pageNo', 'pageSize', 'total', 'continues'],
      // 计算属性
      computed: {
        // 总共多少页
        totalPage(){
            // 向上取整
            return Math.ceil(this.total/this.pageSize)
        },
        // 计算出连续的页码的起始数字与结束数字[连续的页码数字：至少是5]
        startNumAndEndNum(){
            const {continues, pageNo, totalPage} = this
            // 先定义两个变量存储起始数字与结束数字
            let start = 0, end = 0
            // 连续的页码数字是5【就是至少5页】，如果出现不正常的现象【就是不够5页】
            // 不正常现象【总页数没有连续页码多】
            if(continues > totalPage){
                start = 1
                end = totalPage
            }else{
                // 正常现象[连续的页码是5，但你的总页数一定是大于5的]
                // 起始数字
                start = pageNo - parseInt(continues/2)
                // 结束数字
                end = pageNo + parseInt(continues/2)
                // 把出现不正常的现象【start数字出现0 | 负数】纠正
                if(start < 1){
                    start = 1
                    end = continues
                }
                // 把出现不正常的显现【end数字大于总页码】纠正
                if(end > totalPage){
                    start = totalPage - continues + 1
                    end = totalPage
                }
            }
            return {start, end}
        }
      }
    }
  </script>
  
  <style lang="less" scoped>
    .pagination {
        text-align: center;
      button {
        margin: 0 5px;
        background-color: #f4f4f5;
        color: #606266;
        outline: none;
        border-radius: 2px;
        padding: 0 4px;
        vertical-align: top;
        display: inline-block;
        font-size: 13px;
        min-width: 35.5px;
        height: 28px;
        line-height: 28px;
        cursor: pointer;
        box-sizing: border-box;
        text-align: center;
        border: 0;
  
        &[disabled] {
          color: #c0c4cc;
          cursor: not-allowed;
        }
  
        &.active {
          cursor: not-allowed;
          background-color: #409eff;
          color: #fff;
        }
      }
    }
    .active{
        background-color: skyblue;
    }
  </style>